Catalytic Ammonia Synthesis over Mo Nitride/ZSM-5

Abstract

Molybdenum nitride species in HZSM-5 are prepared by the reaction of ammonia with MoO_x, which is pre-exchanged into the channel of HZSM-5. Both the processes of solid exchange of molybdenum oxide with the zeolite and the ammonia reaction are monitored by mass spectrometry. The Mo/N ratio of the MoN_xspecies in the Mo nitride/HZSM-5 is close to 2, as measured by temperature-programmed oxidation. The MoN_xspecies are more stable than bulk Mo₂N against oxidation, due to the interaction between the molybdenum nitride species and the charged zeolite framework. The MoN_xspecies, of which the dispersion is found to be greater than 90 %, are very active in ammonia synthesis and the catalytic activity is much more stable than that of bulk Mo₂N. The reaction pressure is much more favorable to ammonia formation on the MoN_x/ZSM-5 catalyst than on bulk Mo₂N. The interaction of nitrogen molecules with the inner electric field of the zeolite, at an equivalent pressure, enhances the reaction of ammonia synthesis.